Heretofore, in regard to a side door or a rear door of a vehicle, it has been attempted to achieve weight reduction, while ensuring rigidity of the door, by forming an inner panel thereof from a steel sheet and forming an outer panel thereof from an aluminum alloy sheet. Matters to be considered in this case include a problem of deformation due to joint of different kinds of metals (dissimilar metals). That is, a steel sheet and an aluminum alloy sheet are different from each other in terms of thermal expansion coefficient. Thus, when a vehicle body is heated up, for example, in a coating baking process during manufacturing, or during parking under the blazing sun, a thermal strain such as flexure is likely to occur in a joined region due to the difference in thermal expansion coefficient. Therefore, in recent, a technique disclosed in the following Patent Literature 1 has been proposed as a joint structure for members of dissimilar metals (dissimilar metal members). This literature describes joining an aluminum roof panel and a roof side rail formed from a steel sheet together at a plurality of positions in a vehicle front-rear direction by non-penetrating rivets, and forming in the aluminum roof panel a bead portion extending along the joined areas (along the vehicle front-rear direction). That is, it is intended to absorb a vehicle width directional strain occurring due to a difference in thermal expansion coefficient between the aluminum roof panel and the roof side rail, by the bead portion formed in the aluminum roof panel.
However, the aluminum roof panel also undergoes thermal expansion in the vehicle front-rear direction. Thus, the technique disclosed in the Patent Literature 1 has difficulty in solving a strain of the aluminum roof panel in an alignment direction of the joined areas (vehicle front-rear direction.)